Device for the storage of a heat evolving material



Jan. 18, 1966 D. w. MONTGOMERY 3,230,373

DEVICE FOR THE STORAGE OF A HEAT EVOLVING MATERIAL Original Filed April17, 1959 g. 34 1 zcififi a 2 g Es o c c ::U I O i... l. J

46 as 50 4a 52 INVENTOR.

Donald W. Montgomery AT TORNEY United States Patent 3,230,373 DEVICE FORTHE STORAGE 0F A HEAT EVOLVING MATERIAL Donald W. Montgomery, Lynchburg,Va., assignor to The Bahcock dz Wilcox Company, New York, N.Y., acorporation of New Jersey Original application Apr. 17, 1959, Ser. No.807,196, now Patent No. 3,046,403, dated July 24, 1962. Divided and thisapplication Apr. 17, 1962, Ser. No. 188,069 The portion of the term ofthe patent subsequent to July 24, 1979, has been disclaimed anddedicated to the Public 5 (Iiaims. (Cl. 250--106) This invention relatesin general to a storage container for a heat evolving material and inparticular to a storage and shipping cask for a heat evolving radiationsource. This application is a division of my copending application,Serial No. 807,196, filed April 17, 1959, and issued on July 24, 1962,as US. Patent No. 3,046,403.

The commercial operation of heterogeneous power reactors will involvethe storage, handling, and transfer of spent fuel elements forreprocessing at approved, designated sites. Thus a commerciallypracticable shipping cask for such service is an important adjunct tothe economic production of nuclear power. This is particularly so sincethe spent fuel elements contain a certain amount of residualradioactivity and will require shielding to prevent radiation damage topersonnel and objects nearby as well as a cooling system to remove theheat released by the spent fuel elements. Lead casks have been used inthe past to provide the shielding with cooling provided by natural heattransfer through the walls of the cask to the atmosphere. While suchapparatus has satisfactorily met the storage and transportation needs ofresearch and development reactors, the probability of handling largerquantities of spent fuel elements from industrial reactors and the highcosts associated with such handling indicates the need for an improvedcask design.

The present invention describes a spent fuel storage and shipping cask,in the design of which the primary objectives are safety and flexibilityof operation combined with economy of storage and shipment. This economyis obtained by making the cask small enough to be shipped on anystandard railroad car and yet large enough to contain enough elements tolower the shipment charge per unit of fuel shipped.

Further, the present invention provides a cylindrical steel vesselembedded in a rectangular cask of radiation shielding material forcontaining the spent fuel elements in conjunction with an exterior heatexchanger for the removal of the heat generated by the decay ofradioactive fission products in the spent fuel. The vessel is adapted tocontain a fluid, such as water, that may be circulated through thevessel and the heat exchanger to conduct the heat from the spent fuelelements to the heat exchanger where the fluid is cooled by aircirculating across the heat exchanger tubes.

Also, it is a provision of the present invention to permitpressurization of the vessel and heat exchange apparatus since they aredesigned to withstand superatmospheric pressures. This permits the heatenergy generated within the vessel to increase the pressure containedtherein should the heat exchange apparatus become incapable of removingall the heat generated. This pressurization could continue for asufficient length of time to permit isolation of the heat exchangeapparatus for repair or replacement of defective parts.

Furthermore, the present invention provides a lining of radiationshielding in association with the pressure vessel 3,236,373 PatentedJan. 18, 1966 to prevent any harmful radiation from the spent fueltherein from escaping the confines of the shipping cask. This lining isarranged to provide a substantially constant thickness of shieldingsurrounding an optimum number of fuel elements contained within theshipping cask with minimum overall outside dimensions.

The various features of novelty which characterize my invention arepointed out with particularity in the claims annexed to and forming apart of this specification. For a better understanding of the invention,its operating advantages and specific objects attained by its use,reference should be had to the accompanying drawings and descriptivematter in which I have illustrated and described a preferred embodimentof the invention.

Of the drawings:

FIG. 1 is a vertical section through the shipping cask and associatedheat exchangers;

FIG. 2 is a plan section taken along line 2-2 of FIG. 1.

In the drawings there is shown the shipping cask 16 comprising avertically elongated pressure vessel 11 of circular cross section havinga lower dished head 12 and terminating at the upper end in an enlargedportion forming a closure flange 14. Mating with this flange 14 andremovably attached thereto, by a plurality of threaded bolts 16 throughan upper closure flange 13, is an upper dished head 20, of which theupper closure flange 18 is an integral part. integral with the interiorof the vessel 11 and extending from the bottom thereof to a positionjust below the closure flange 18 is a lining 22 of radiation shieldingmaterial. This lining 22 has an outer surface conforming to the innersurface of the vessel 11 and an inner surface which defines a verticallyelongated rectangular cavity 24. This cavity is adapted to accommodate acooling fluid, such as water, for cooling the spent fuel elements asalso contained therein. The top of this cavity 24 is closed by aremovable shielding plug 28 which provides radiation shielding over thetop of the spent fuel elements 26 and yet allows access to the cavity.The joint between the shielding plug 28 and the inner lining 22 isprovided with a series of setbacks 30 which reduce the possibility ofradiation leakage.

Enclosing the lower dished head 12 and extending exterior to the vessel11 up to the top of the inner lining 22 is an outer lining 32 ofradiation shielding material. This lining 32 has an inner surfaceconforming to the outer surface of the vessel 11 and an outer surface ofthe same general cross section as the inner rectangular cavity 24. Thecorners of these two rectangular cross sectional areas are diagonallyaligned so as to provide the cavity 24 with a radiation shield ofsubstantially constant cross section in a minimum of overall dimensions.At the same time a rectangular space is provided within the circularvessel 11 for optimally stacking spent fuel elements. All of theshielding in contact with the cooling fluid in the vessel is providedwith a cladding 25 of stainless steel.

Exterior of the vessel 11 and shielding 32 are heat exchangers 34comprising an inlet header 36 and an outlet header 38 connected by aplurality of heat exchange tubes 41). A specific example of the typeheat exchanger referred to is a horizontal fin tube steam condenser. Theinlet header 36 is connected to the interior of the vessel 11 by a riserline 42 which opens into the upper portion of the vessel above theshielding plug 23. The shielding plug 28 is provided with a plurality ofconduits 44 therethrough which communicate with the shielded cavity 24and provide flow passes between the cavity and the riser line 42. Theseconduits 44 are further provided with an offset between the top and thebottom of the shielding plug 28 which reduces the possibility of theescape of radiation from the shielded cavity 24. An outlet header 38 isconnected to the interior of the vessel 11 by a downcomer line 46 whichextends through the outer shielding 32 and the vessel shell and thendown through the inner shielding 22 before terminating at the bottom ofthe cavity 24. Both the riser and downcomer lines, 42 and 46, areprovided with valves 48 and couplings 50 adjacent the headers, 36 and38, to permit the isolation and removal of the heat exchanger. The heatexchangers 34 are also removably connected to the vessel 11 via thesupports 52.

Suitable handling means, such as lifting lugs, etc. (not shown) areprovided for the entire apparatus, as well as for the individualcomponents, to facilitate handling during loading and shipment.

The present invention contemplates the use of a fan or other such blowermeans (not shown) to circulate air over the heat exchanger tubes 40 toremove the heat from the fiuid therein. It is important that the blowersnot be directly connected to the underside of the heat exchangers orotherwise located so close to them as to restrict normal convection fiowof air should the fans be out of operation.

In operation, the spent fuel elements 26 would be loaded into theshipping cask within the shielded cavity 24. The cask would then befilled with water to a level just below the shielding plug 28 and theshielding plug would be fitted into place. Water is used because otherliquids are often objectionable in the fuel chemical reprocessingoperation. The use of water also eliminates the necessity of anintermediate heat transfer fluid since the water will not becomeradioactive during circulation. The upper head 20 of the vessel 11 wouldthen be attached and sealed and the valves 48 closed. The cask 10 wouldthen be loaded onto a railroad car and the heat exchangers attached. Inthe interim, heat generated by the spent fuel elements would pressurizethe water in the cask. After the heat exchangers are attached, thevalves 48 would be opened allowing the steam generated to circulatethrough the heat exchangers where it would be condensed and returned tothe bottom of the cask. The flow path of the fluid in cooling the spentfuel elements would be as follows: The spent fuel elements wouldgenerate steam in the water within the shielded cavity 24. This steamwould rise and pass through the shielding plug 28 via the conduits 44and enter the inlet header 36 via the rise liner 42. The steam wouldthen pass through the tubes 40 where it would be condensed by the aircirculating exterior thereto. The condensed steam would then passthrough the outlet header 38 and return to the shielded cavity 24 viathe downcorner line 46. The blower means could then be put intooperation to aid in cooling the heat exchanger tubes so the interior ofthe cask could be maintained at a pressure near atmospheric.

To eliminate any criticality hazard from the spent fuel, basket inserts54 of a neutron absorbing material are arranged between the spent fuelelements 26. These baskets also provide for shipping broken or damagedfuel elements and reduce the hazard of inadvertently shipping a highlyradioactive fuel element that would approach criticality if the neutronabsorbing material were not present. Further, the baskets aid in thehandling of the fuel elements and prevent their shifting duringshipment.

In the event of a power loss to the fans, the cask would pressurize toapproximately 50 p.s.i.g. and would be able to operate indefinitely inthis manner due to the heat removal therefrom by the natural circulationof air over the heat exchanger tubes. If, during this operation withoutfans, one of the heat exchangers should rupture or be damaged, thedamaged heat exchanger would be isolated from the system by the valves48. During this period the cask pressure would increase to approximately310 p.s.i.g. and would continue in operation with the heat being removedthrough the remaining heat exchanger. In the event of damage to bothheat exchangers, they would be isolated and the cask would pressurize toabout 480 p.s.i.g., the pressure setting of the safety valve (notshown). Operation under this extreme condition could be sustained forapproximately four hours before all the coolant would be releasedthrough the safety valve, how ever, during this time one or both of theheat exchangers could be replaced and the former operating conditionsrestored. Thus, a system with these operating characteristics hasinherent safeguards which contribute to safety and ease of operation,since a major malfunction of equipment must occur before operatingdifficulties are encountered.

While in accordance with the provisions of the statutes I haveillustrated and described herein the best form and mode of operation ofthe invention now known to me, those skilled in the art will understandthat changes may be made in the form of the apparatus disclosed withoutdeparting from the spirit of the invention covered by my claims, andthat certain features of my invention may sometimes be used to advantagewithout a corresponding use of other features.

What is claimed is:

1. In a device for the storage of a heat evolving radiation sourcecomprising a pressure vessel with a circular cross section having anopening therein, a removable closure for said opening, said radiationsource contained within said pressure vessel, and a lining of radiationshielding material associated with the inner surface of said pressurevessel and arranged to envelop said radiation source.

2. In a device for the storage of a heat evolving radiation sourcecomprising a pressure vessel with a circular cross section having anopening therein, a removable closure for said opening, said radiationsource contained within said pressure vessel, and an inner and outerlining of radiation shielding material associated with the inner andouter surfaces of said pressure vessel and arranged to envelop saidradiation source.

3. In a device for the storage of a heat evolving radiation sourcecomprising a pressure vessel with a circular cross section having anopening therein, a removable closure for said opening, said radiationsource contained within said pressure vessel, and an inner and outerlining of radiation shielding material associated with the inner andouter surfaces of saidpressure vessel and arranged to envelop saidradiation source, said lining of radiation shielding material having aremovable portion coincident with said removable pressure vessel closureto permit access to the interior of said shielding.-

4. In a device for the storage of a heat evolving radiation sourcecomprising a pressure vessel with an opening therein, a removableclosure for said opening, said radiation source contained within saidsaid pressure vessel and having a rectangular cross section, saidpressure vessel having a circular cross section, and an inner and outerlining of radiation shielding material associated with the inner andouter surfaces of said pressure vessel and arranged to envelop saidradiation source, said lining of radiation shielding material having aremovable portion coincident with said removable pressure vessel closureto permit access to the interior of said shielding, said inner shieldinghaving a rectangular cavity therein to receive said rectangularradiation source, the outer surface of said inner shielding conformingto the inner surface of said cylindrical pressure vessel.

5. In a device for the storage of a heat evolving radiation sourcecomprising a pressure vessel with an opening therein, a removableclosure for said opening, said radiation source contained within saidpressure vessel and having a rectangular cross section, said pressurevessel having a circular cross section, and an inner and outer lining ofradiation shielding material associated with the inner and. outersurfaces of said pressure. vessel and arranged to envelop said radiationsource, said lining of radiation shielding material having a removableportion coincident with said removable pressure vessel closure to permitaccess to the interior of saidshielding, said inner shielding having arectangular cavity therein to receive said rectangular radiation source,the outer surface of said inner shielding conforming to the innersurface of said cylindrical pressure vessel, said outer shielding havinga rectangular cross section enclosing said cylindrical pressure vesselwith the corners thereof diagonally aligned With the corners of saidrectangular cavity of said inner shielding to provide shielding ofsubstantially uniform thickness for said rectangular radiation sourcecontained within said cylindrical pressure vessel.

References Cited by the Examiner UNITED STATES PATENTS OTHER REFERENCESRadiation Shielding, Price et al., published by Perga- 10 mon Press, NewYork, New York, 1957, page 233.

RALPH G. NILSON, Primary Examiner.

ARCHIE R. BORCHELT, Examiner.

1. IN A DEVICE FOR THE STORAGE OF A HEAT EVOLVING RADIATION SOURCECOMPRISING A PRESSURE VESSEL WITH A CIRCULAR CROSS SECTION HAVING ANOPENING THEREIN, A REMOVABLE CLOSURE FOR SAID OPENING, SAID RADIATIONSOURCE CONTAINED WITHIN SAID PRESSURE VESSEL, AND A LINING OF RADIATIONSHIELDING MATERIAL ASSOCIATED WITH THE INNER SURFACE OF SAID PRESSUREVESSEL AND ARRANGED TO ENVELOP SAID RADIATION SOURCE.